The present invention relates to image sensors, and more particularly, towards color filter structure having reduced stress.
Image sensors are electronic integrated circuits that can be used to produce still or video images. Solid state image sensors can be either of the charge coupled device (CCD) type or the complimentary metal oxide semiconductor (CMOS) type. In either type of image sensor, a light gathering pixel is formed in a substrate and arranged in a two-dimensional array. Modern image sensors typically contain millions of pixels to provide a high resolution image. An important part of the image sensor are the color filters and micro-lens structures formed atop of the pixels. The color filters, as the name implies, are operative, in conjunction with signal processing, to provide a color image. The micro-lenses serve to focus the incident light onto the pixels, and thus to improve the fill factor of each pixel.
While the technology underlying the formation of color filters is relatively mature, there are still issues that may arise, particularly at higher integration densities. For example, U.S. Pat. Nos. 6,297,071, 6,362,513, and 6,271,900 show the current state of the color filter art. In the prior art, the color filter is typically formed from an organic material. It has been observed that when the color filter is formed atop of the substrate containing the pixel, physical cracking of the substrate may occur. It is believed that the interface of the organic color filter with the substrate causes stress, which in turn results in cracking.
The cracking of the substrate is undesirable insofar as it may cause defects in the image sensor.